In general, for the manufacture of a semiconductor integrated circuit, various kinds of processes such as a film forming process, an etching process, an oxidizing process, a diffusing process, a modifying process and a natural oxide film removing process are performed with respect to a semiconductor wafer composed of a silicon substrate or the like. These processes are performed in a single-wafer-type processing apparatus that processes wafers one by one or in a batch-type processing apparatus that processes a plurality of wafers at a time. For example, if these processes are performed in a so-called vertical batch-type processing apparatus, semiconductor wafers are first transferred from a cassette capable of accommodating a plurality of, e.g., twenty five, semiconductor wafers, to a vertical wafer boat and are supported on the vertical wafer boat in multiple stages.
The wafer boat can hold, e.g., about 30 to 150 wafers, depending on the wafer size. The wafer boat is loaded into an evacuable processing vessel from the lower side thereof. Thereafter, the interior of the processing vessel is kept gas-tight. Then, a predetermined heat treatment is carried out while controlling various kinds of process conditions such as a flow rate of a process gas, a process pressure and a process temperature.
As one of the factors that improve the properties of the semiconductor integrated circuit, it is important to improve the properties of an insulating film existing in the integrated circuit. SiO2, PSG (Phospho Silicate Glass), P (Plasma)-SiO, P (Plasma)-SiN, SOG (Spin On Glass), Si3N4 (silicon nitride film) and the like are generally used as the insulating film existing in the integrated circuit. In particular, the silicon nitride film tends to be extensively used because the silicon nitride film is superior in insulating property to a silicon oxide film and because the silicon nitride film sufficiently serves as an etching stopper film, an interlayer insulating film or a gate sidewall film.
In recent years, with a view to improve the properties of a circuit element, there is a strong demand for a much lower dielectric constant (low-k) and an increased resistance to etching. Under these circumstances, seeing that an intended process is available without exposing a wafer to a higher temperature even in a so-called vertical batch-type processing apparatus, there has been proposed a method in which a film is formed by repeating formation of one to several layers at an atomic level or repeating formation of one to several layers at a molecular level while intermittently supplying source gases. Such a film forming method is generally called ALD (Atomic Layer Deposition).
In an effort to lower the dielectric constant of a film and to increase the etching resistance of a film as mentioned above, research is being carried out on a technology of adding boron, carbon or oxygen to a base silicon nitride film. Recently, attention is paid to a SiOCN film obtained by adding oxygen and carbon to a silicon nitride film.
In a SiOCN film formed by a method of related art, the concentration of added oxygen or the concentration of added carbon is not sufficiently high. In a method of forming a SiOCN film as a whole by alternately forming a SiCN film and a SiO film, oxygen serving to reduce a dielectric constant can be added in a sufficient amount. However, the method suffers from a problem in that the concentration of carbon which serves to increase an etching resistance still remains insufficient.